Spin-on filters are employed in a variety of applications, including hydraulic systems and engine lubrication systems. Suck filters generally include a filter element with a can or filter housing, having a closed end and an open end. A cover mounts on the open end of the filter housing and,permits attachment of the filter housing to a filter head assembly on any given piece of equipment. Fluid passes from the filter head assembly through a first opening in the filter head assembly into the housing for filtration. A second opening in the filter head assembly receives the filtered fluid from the housing through a second opening in the housing. Various seals typically exist to provide fluid tight seals between the various components. After use, the spin-on filters are typically replaced with new filters.
Although satisfactory in low and medium pressure applications, many conventional spin-on filters are not particularly suitable for use in high pressure applications where pressures may exceed 1000 psi or more. As fluid systems pressures increases, conventional spin-on filters are no longer satisfactory.
Various designs exist Which provide spin-on filters capable of satisfactory performance in the high pressure environment. U.S. Pat. No. 4,369,113, issued to Donaldson Company, Inc. relates to an improved high strength spin-on filter capable of surges and spikes up to 1000 psi or more. U.S. Pat. Nos 4,743,374 and 5,104,537 both issued to Donaldson Company, Inc. relate to filters which provide for improved fatigue and pressure capacity.
Often, the machinery benefits if the high pressure filter provides a by-pass valve to divert the high pressure fluid when the filter element is blocked. As the filter operates, sediment, or particles build up in the filter element, which eventually block fluid flow through the filter element. However, the machinery, which the filter mounts on, continues to provide fluid pressure in a direction towards the filter. Without a by-pass filter, pressure builds up in the filter assembly and may cause serious damage to the machinery.
By-pass filters have been used in low pressure filters. For Example Cudaback U.S. Pat. No. 4,872,976 issued Oct. 10, 1989, discloses a hinged flapper biased against a passage. The flapper rotates from a normal position to a by-pass position. Similarly Brownell U.S. Pat. No. 4,853,118 issued Aug. 1, 1989, discloses a hinged flap disposed against a passage. Each of these designs does not accommodate the high pressures contemplated by the present applications.
By-pass filters, including the filter head assembly, of the prior art provide arrangements in which high pressure fluid flows in an alternative path when the filter element is blocked. However, in the field of high pressure filters the by-pass valve is not integral with the spin-on filter itself. Often the by-pass valve is located in the filter head assembly so that the valve can withstand the high pressures when the by-pass valve was closed. See, for example, Fisher et al. U.S. Pat. No. 4,883,083 issued Nov. 28, 1989 entitled "Relief Valve Assembly; Piston Member From Same and Filteir Head Assembly Incorporating the Same".
Efforts made to include a by-pass filter in the spin-on filter itself centered on placing the by-pass valve at the bottom of the filter housing. However, this arrangement presents serious concerns. During operation sediment builds up in the bottom of the filter housing. When the by-pass valve engages, the fluid flows through the bottom of the filter housing, before returning to the machinery. By drawing the fluid through the bottom of the filter housing, the sediment previously accumulated at the bottom of the filter housing is Carried back into the machinery. The returned sediment causes unnecessary wear on the machinery.
Also, placing the by-pass filter at the bottom of the filter housing forces the fluid to travel the full length of the filter. Fluid flowing the entire length of the filter housing creates unnecessary inefficiencies. For example, see the McBroom et al. reference, U.S. Pat. No. 4,428,834, issued Jan. 31, 1984 to Donaldson Company, Inc. entitled "Fluid Filter With Integral Viscous Damper". The present invention solves these and other problems by providing a unique by-pass arrangement.